This invention relates to circuitry for use in transmitters in differential or single-ended signalling circuitry or systems.
In order to compensate for losses in the transmission of data signals—especially in digital systems operating at high speeds with low voltage signals—it may be desired to give the data signals what is called pre-emphasis. Pre-emphasis is extra power (usually extra voltage, but extra current may be an equivalent) immediately adjacent each transition in the level of the digital data signal. Pre-emphasis (provided by the circuitry transmitting the signal) helps to compensate for losses in transmission of the signal to receiver circuitry, and thereby helps the receiver circuitry respond more correctly to each transition in the transmitted signal.
Known pre-emphasis circuitry (e.g., for low voltage differential signalling (“LVDS”)) may benefit from improvement, especially as systems attempt to use lower and lower power supply voltages. For example, such known LVDS pre-emphasis circuitry may employ both PMOS and NMOS transistors in an H-bridge type of topology, but PMOS transistors are inherently slower in switching and take more layout area. Also, this type of output driver circuitry needs common-mode feedback circuitry for better control of common mode swing under process corners. In addition, this type of circuitry requires higher supply voltages due to the stacked transistors, and thus headroom is an issue.